The invention relates to the use of roof mounted oxy-fuel burners for glass melting. This invention further relates to the use of at least one oxygen-fuel burner that utilizes internal or external combustion staging in the roof of a glass melting furnace. The invention applies both to 100% oxygen-fuel fired furnaces and to furnaces heated by electric or non oxygen-fuel means, such as air-fuel burner(s) or their combinations.
In one embodiment, this invention relates to the use of at least one oxygen-fuel burner in the roof of a glass melting furnace to boost production capacity or maintain current production capacity with either reduction of electro-boost or as a result of deterioration of existing heat recovery equipment such as recuperators or regenerators. The process involves the replacement of a portion of existing or previously existing air-fuel or electrical energy capacity with oxy-fuel energy. With the exception of end-fired regenerative furnaces and electric furnaces, the process involves the blocking of regenerative ports or isolation of recuperative burners. In particular the design selection, angling and positioning of the burners over the raw batch materials entering the furnace improves the rate of melting, increases product yield, provides better energy efficiency and improves glass quality. Accurate control of the stoichiometric ratio of combustion in the burner, rich-lean interaction of burners, and furnace zonal fuel/oxygen staging are used to optimise heat transfer while minimizing oxides of nitrogen and sulfur dioxide emissions.
Regenerative, recuperative, electric and direct fired furnaces have been commonly involved in the manufacture of glass and related frit products.
Air-fuel regenerative furnaces fall into two categories: cross-fired and end-fired. Cross-fired regenerative furnaces have multiple ports, typically three to eight on each side of the furnace that connect to either a common or compartmentalized regenerator to preheat the combustion air. The regenerators, which come in various shapes and sizes, reverse every 15-30 minutes dependent on furnace operation. During each reversal cycle combustion air from a fan passing through one passage in a reversal valve enters the base of the regenerator on one side of the furnace and is preheated prior to entering the ports which connect to the furnace. Fuel in the form of oil and/or gas is injected either under, over, through or side of port to produce a flame which is combusted in the glass melting furnace. The hot products of combustion exit the furnace through the opposing side port, down through the regenerator checker bricks, releasing heat and then exiting to the exhaust stack through a second passageway in the reversal valve. As the incoming combustion air-side regenerator cools, the exhaust regenerator heats until the reversal valve reverses and combustion air enters the previously hot exhaust regenerator.
The glass is melted partly due to the radiation of the air-fuel flame but mainly by re-radiation from the roof and walls which are heated by the products of combustion. To obtain higher furnace glass production capacity, many furnaces use electric boost by means of electrodes immersed in the glass. This is costly and can cause damage to the glass contact tank walls. Through time, regenerators can become blocked due to thermal/structural damage and/or carry-over of raw glass forming materials, also known as batch materials or batch, or condensation of volatile species released from the glass batch. As the regenerators start to block or fail, the preheat temperature of the air in the furnace will decrease, and the atmospheric pressure within the furnace will increase, reducing the thermal efficiency of the furnace. More fuel and combustion air would be required to maintain the same glass production rate. More importantly, because of the increase in furnace pressure, the rate of glass production must be decreased so as not to damage the refractory materials that make up the superstructure of the furnace.
To recover production capacity lost to preceding regenerator issues or to increase production in a non-encumbered furnace, oxygen has been used by four means: general air enrichment with oxygen, specific oxygen lancing under the port flames, installation of an oxy-fuel burner between first port and charging end wall, and water-cooled oxy-fuel burners installed through the port. The capacity increases from these technologies are limited by access, process requirements or refractory temperature limits.
The End-Fired Regenerative furnace is similar in operation to a cross-fired furnace; however, it has only two ports in the end wall which connect to individual regenerators. Regenerator deterioration can occur by the same mechanism as in cross-fired furnaces and similarly, electric and oxygen boost is utilized.
To recover production capacity lost to the aforementioned regenerator issues or to increase production, oxygen has been used by three means: general air enrichment with oxygen, specific oxygen lancing under the port and installation of oxy-fuel burners through the furnace. These technologies are typically capacity limited due to temperature limitations within the furnace, because of location and concerns for overheating of the furnace.
The recuperative furnace utilizes at least one recuperator type heat exchanger. Unlike the regenerator, the recuperator is continuous with a hot concurrent flow heat exchanger where exhaust gases preheat combustion air, which is ducted to individual air fuel burners along the sides of the furnace. Recuperative furnaces can also use electric boost. As with regenerative furnaces, recuperators can start to lose their efficiency and ability to preheat the air. They can become blocked or develop leaks between the walls separating the combustion air and exhaust gases.
To recover production capacity lost from the aforementioned recuperator issues or to increase production, oxygen has been used by three means: general air enrichment with oxygen, specific oxygen lancing under the air fuel burners and installation of oxy-fuel burners either through the furnace breast walls. These technologies are typically limited on capacity because of burner location limitations and concerns for overheating of the furnace.
Direct fired furnaces do not utilize preheated air and are therefore less efficient than the preceding examples of furnace design. To improve thermal efficiency or increase production capacity, side wall oxy-fuel burners have replaced air fuel burners.
Electric furnaces or furnaces which utilize electricity for the majority of melting are typically costly to operate and are subject to a shorter campaign life than the typical fossil fuel fired furnaces. Once designed, it is difficult to increase the production capacity. This invention relates to what are commonly referred to in the industry as hot top and warm top electric furnaces and does not apply to cold top furnaces.
U.S. Pat. No. 5,139,558 to Lauwers discloses the use of a water cooled, high-momentum roof-mounted auxiliary oxygen fired burner in a glass melting furnace, which is directed to the interface of the melted and solid glass forming ingredients at an angle directed upstream relative to the glass flow, whereby the solid glass forming ingredients are mechanically held back, thus being prevented from escaping the melting zone.
U.S. Pat. No. 3,337,324 to Cable discloses a process for melting batch material in a glass furnace using a burner positioned to fire substantially down over the feed end of a water-cooled furnace.
In the past, roof-mounted burners were considered in the glass industry, but were disregarded. It was perceived that the heat release from roof mounted burners was too great, resulting in the melting of the furnace crown (roof). In addition, high momentum flames from the burners would blow the batch materials around, harming the furnace walls, and generating a layer of gaseous bubbles, commonly referred to as foam, on the glass melt surface.
Recently, it has been proposed to install roof-mounted oxy-fuel burners in refractory lined glass melters. These burners are directed downwards at an angle greater than 45xc2x0 with respect to the surface of the glass forming material at a controlled velocity so as not to transport loose batch material into the furnace atmosphere, and are further controlled such that a generally columnar fuel and oxygen flow combusts proximate to the top surface of the glass forming material, to produce a flame that impinges the surface of the raw glass forming material. This permits a significant increase in heat transfer into the glass, while maintaining refractory temperatures within safe operating limits, and avoiding the overheating of the roof and walls of the furnace. This technology approach, of using roof-mounted burners (non-staged) as the primary source of heat in a glass melting furnace having no regenerators or recuperators, is described in U.S. patent application Ser. No. 08/992,136 to LeBlanc, which is incorporated herein by reference as if fully written out below.
The design of an oxygen fuel burner with integral staging is disclosed in U.S. Pat. No. 5,458,483 to Taylor. Its use in a roof mounted configuration was not contemplated, however.
It is desirable to provide processes for the staging of combustion in embodiments that improve heat transfer and/or lower emissions of oxides of nitrogen, in the operation of at least one oxy-fuel burner mounted in the roof of a glass melting furnace.
The present invention relates to both 100% oxy-fuel glass furnaces and oxy-fuel boosting of air-fuel furnaces with or without the use of regenerators or recuperator heat recovery devices and/or oxygen enrichment. Consequently, the present invention relates to both the modification of existing glass furnaces and newly designed, dedicated purpose glass furnaces.
According to the present invention, glass melting furnaces of all designs can be boosted using at least one roof-mounted oxygen fuel burner(s) positioned over the raw batch materials as the materials enter the furnace to improve the rate of melting and improve glass quality and/or glass product yield. Because of the increased rate and yield of the glass melting generated by the design and positioning of these burners, depending on furnace condition and type, at least one or more of the following can be achieved: increased glass production, improved glass quality, reduction in electric boost, recovery of production lost due to inefficient heat recovery (i.e., blocked regenerators), reduction of oxygen use by replacing oxygen enrichment of the furnace atmosphere, reduction of oxygen use by replacing oxygen lancing, reduction of oxygen use by replacing conventional oxy-fuel burners positioned through the walls of a glass furnace, reduction in furnace superstructure temperature, increased furnace campaign life, improved energy efficiency, reduction in emissions of oxides of nitrogen and oxides of sulfur, reduction in fossil fuel usage, reduction in recycled glass cullet, control of exit glass temperature, and increased product glass yield.
This invention may be applied to the following types of furnaces. In hot top electric furnace applications of this invention, at least one oxygen-fuel burner will be mounted in the roof of the furnace. In cross-fired regenerative furnaces applications of this invention may sometimes necessitate at least one pair of the opposing ports to be fully or partially blocked or isolated. In end-fired regenerative furnace applications of this invention, at least one oxygen-fuel burner will be mounted in the roof of the furnace and the combustion air flow will be reduced by a portion of the original design maximum flow. In all recuperative furnace applications of this invention, at least one oxygen-fuel burner will be mounted in the roof of the furnace. In multi-burner furnaces, wall mounted burners adjacent to the roof mounted burners should be removed and the air supply isolated. In single burner or single port applications, the combustion air flow will be reduced by a portion of the original design maximum flow.
In all direct fired furnace applications of this invention, at least one oxygen-fuel burner will be mounted in the roof of the furnace. In multi-burner furnaces, wall mounted burners adjacent to the roof mounted burners should be removed and the air supply discontinued. In single burner or single port applications, the combustion air flow will be reduced by a portion of the original design maximum flow.
In all the above cases the scope of the invention is effectively the same: glass melting which was previously performed by air-fuel or oxy-fuel including but not exclusive of furnaces that utilize electric boost or conventional oxygen boosting methods, is replaced by roof-mounted oxy-fuel burners positioned over the raw batch materials entering the furnace to improve the rate of melting and/or improve glass quality and/or glass product yield. Because of the ability to position these burners at specific locations, increased heat transfer to the unmelted raw batch materials is achieved.
In all cases, at least one roof-mounted oxy-fuel burner is positioned over the raw batch materials entering the furnace to improve the rate of melting and improve glass quality, and in all multi-port and multi-burner air fuel applications at least one pair of ports or pair of burners are isolated. In all single port and single burner applications, the combustion air and fuel are reduced to a portion below the maximum design. The more efficient roof mounted burners provide energy to replace the conventional energy removed from the process and the additional energy required to achieve the desired process requirements. The positioning of the burners over the raw batch entering the furnace improves the rate of melting. The stoichiometric oxygen and fuel ratios and flow characteristics of the roof-mounted burners and remaining air-fuel burners can be controlled so as to minimize the emission of nitrous oxide and sulfur dioxide from the glass furnace.
A further embodiment of this invention relates to the use of at least one oxygen-fuel burner that utilizes internal or external combustion staging, positioned in the roof of a glass-melting furnace. This embodiment applies both to 100% oxygen-fuel fired furnaces and to furnaces heated by electric or non-oxygen-fuel (such as air-fuel burner) means. The application to oxygen-fuel fired furnaces provides an increased rate of melting, resulting in at least one of an improvement in glass quality, glass production capacity and energy efficiency (by reduction in either fossil fuel- or electro-boost) per unit output of glass. The application of the present invention to non-oxygen fuel furnaces permits one to improve glass quality, and to boost production capacity or maintain current production capacity with either reduction of electro-boost or despite the deterioration of existing heat recovery equipment. In retrofit installations, the process involves the supplement or replacement of a portion of existing or previously existing oxygen-fuel, air-fuel or electric energy capacity with oxy-fuel energy through at least one oxygen fuel burner with integral or external combustion staging located in the roof of the furnace.
In new glass furnace installations, the present invention permits the use of 100% oxy-fuel burners, including at least one roof mounted oxy-fuel burner for which combustion is integrally or externally staged. Optionally, all burners are roof mounted.
The present invention therefore provides a method of melting glass forming material in a glass melting furnace, said furnace having a back wall, breastwalls above sidewalls, and a downstream front wall connected to a roof, wherein at least one batch charger for charging glass forming batch material is contained in at least one of the back wall and the sidewall, comprising:
providing at least one oxy-fuel burner in the roof of said furnace over said batch material, wherein said at least one oxy-fuel burner is adapted for staged combustion;
providing a flow of fuel to said at least one oxy-fuel burner;
providing a flow of gaseous oxidant in association with said at least one oxy-fuel burner;
injecting the fuel and the oxidant into the furnace; and,
combusting said fuel from at least said one oxy-fuel burner such that at least a portion of combustion is effected in the vicinity of said glass forming material to enhance convective and radiative transfer of heat to said glass forming material without substantially disturbing said glass forming material.
In one embodiment the invention provides a method of melting glass forming material in a glass melting furnace, said furnace having a back wall, breastwalls above sidewalls, and a downstream front wall connected to a roof, wherein at least one batch charger for charging glass forming batch material is contained in at least one of the back wall and the sidewall, comprising:
providing at least one oxy-fuel burner in the roof of said furnace over said batch material;
providing a flow of liquid fuel to said at least one oxy-fuel burner;
providing a flow of gaseous oxidant in association with said at least one oxy-fuel burner;
injecting the fuel and the gaseous oxidant into the furnace; and,
combusting said fuel.
In this embodiment the one oxy-fuel burner may be adapted for staged combustion, including
combusting said fuel from at least said one oxy-fuel burner such that at least a portion of combustion is effected in the vicinity of said glass forming material to enhance convective and radiative transfer of heat to said glass forming material without substantially disturbing said glass forming material.
In another embodiment, the invention provides a method of melting glass forming material in a glass melting furnace, said furnace having a back wall, breastwalls above sidewalls, and a downstream end front wall connected to a roof, wherein at least one batch charger for charging glass forming batch material is contained in at least one of the back wall and the sidewall, comprising:
providing at least one oxy-fuel burner in the roof of said furnace over said batch material, wherein said at least one oxy-fuel burner is adapted for fuel staged combustion and contains at least one outer oxidant injector and two inner fuel injectors, the innermost fuel injector being adapted for high velocity fuel injection and the other fuel injector, disposed between the innermost fuel injector and the outer oxidant injector, being adapted for lower velocity fuel injection;
providing a flow of fuel to said at least one oxy-fuel burner, wherein the flow of fuel through the innermost fuel injector has a higher momentum than the flow of fuel through the other fuel injector;
providing a flow of gaseous oxidant to the outer oxidant injector, having a lower momentum than the flow of fuel through the innermost fuel injector;
combusting said fuel from at least said one oxy-fuel burner such that at least a portion of combustion is effected in the vicinity of said glass forming material to enhance convective and radiative transfer of heat to said glass forming material without substantially disturbing said glass forming material.
In another embodiment, the present invention provides an oxy-fuel burner comprising at least one outer oxidant injector and two inner fuel injectors, the innermost fuel injector being adapted for high velocity fuel injection and the other fuel injector being adapted for lower velocity fuel injection.
In a further embodiment, the present invention provides a method of melting batch material in a glass furnace having regenerators, recuperators and/or electric boost, said furnace having sidewalls, a back wall, a front wall and a roof comprising:
providing at least one burner in the roof of said furnace over said batch material;
providing a flow of gaseous oxidant to said at least one burner;
providing a flow of gaseous fuel to said at least one burner;
generating a flame from at least said one burner said flame having a velocity sufficient to maximize transfer of heat from said flame to said batch material without substantially disturbing said batch material, and,
providing additional oxygen to complete combustion at or near the surface of said batch material from at least one oxygen injector in the roof of said furnace.